A diffuser plate using a microlens array is used as screens such as a head-up display and a laser projector. Using a microlens array is advantageous in that it is possible to suppress speckle noise of laser light compared with using a diffuser plate such as a translucent plate or a frosted glass.
Patent Literature 1 discloses an image forming device including a diffuser plate using a laser projector that has laser light as a light source and projects a video which is an array of a plurality of pixels and a microlens array in which a plurality of microlenses are placed in an array. Using a microlens array makes it possible to appropriately diffuse incident light and flexibly design a necessary angle of diffusion.
Patent Literatures 2 and 3 and Non Patent Literature 1 disclose a screen using two microlens arrays. In the case of using a single microlens array, luminance irregularity and color irregularity are likely to occur. Patent Literatures 2 and 3 and Non Patent Literature 1 describe that, with use of two microlens arrays, it is possible to suppress the occurrence of luminance irregularity.
Further, Patent Literature 3 discloses that, by using one microlens array where microlenses having different properties are placed, it is possible to suppress the occurrence of luminance irregularity due to diffracted light and interfering light caused by the periodic structure.
Patent Literature 4 discloses a method for improving luminance irregularity and color irregularity that occur due to diffraction spots caused by the periodicity of a microstructure by placing a piston form (raised part) having a vertical side surface on a microlens and by randomly distributing at least one of parameters that define the shape or position of a microstructure according to a predetermined probability density function.